Current methods of tapping, or forming threads in a hole, generally use a hard steel tap with a tapered threaded first end that cuts the threads as it is rotated at a second end. Longitudinal grooves, or flutes, which may be straight or helical, interrupt the spiral thread form to generate cutting elements, and to provide clearance space for the chips generated by the cutting elements. Binding of the tap requires increasing torque at the driving end to advance it. The increased twisting of the tap may break it, often leaving the cutting end broken and stuck in the hole. This not only results in loss of the tap, but often means scrapping the part due to the high cost of removal of the broken tap. After a hole is tapped, the tap is removed by reverse rotation.
Because of the danger of tap breakage, it is common practice to periodically reverse rotate to break off the chips.
The method of forming internal threads in workpieces that must be hardened, such as in steel alloy, begins when a tap drill bore is drilled into the soft workpiece and then a tap would be used to cut out the internal threads. Then, after the thread is completed, the workpiece would be subjected to heat treatment to harden the workpiece material. When attempts have been made to form internal threads in a hardened workpiece, the machining operation was very difficult, and the taps would break and fail. Breakage is almost certain when tapping small diameter holes, because the web of the tap with it's small cross section is much weaker and less resistant to the required cutting torque.
When workpiece materials such as steel alloys are heat treated after internal threads are made, they have a tendency to cause the threads and or the workpiece surfaces to deform, making true thread form and accurate location difficult to control.
There is a need in the industry for a tapping system that can quickly manufacture internal threads within an acceptable tolerance in hard workpieces.
The present invention provides a method of tapping a hole in a hard workpiece wherein the internal threads are formed quickly and with precision. These and other objects and advantages of the invention, as well as the details of illustrative embodiments, will be more fully understood from the following specification and drawings.